The use of wind turbines for converting wind energy to electrical energy is becoming more and more popular as we move toward alternative energy sources. Wind turbines of current design are typically mounted atop towers so as to place the turbines in optimal locations for receiving wind energy. As wind turbines get higher and higher, the demand for insuring the safety of employees working daily in the nacelle of the tower of the wind turbine also gets higher. Indeed, such towers are now constructed to heights of 60 meters or more. Maintenance of the wind turbine which is mounted at the top of such a tower requires that service personnel ascend the interior of the tower structure in one of two ways. The first way is to manually ascend the tower using a ladder system that is situated within the tower. The second way is to use a work cage that is electro-mechanically operable, much like an elevator, to move upwardly and downwardly within the nacelle or tower. In areas where several wind turbine towers are located, such as on a wind turbine “farm,” a service technician may be required to ascend and descend several towers during a single work cycle. Experience shows that service technicians perform better quality service when they are transported in a lift or work cage as opposed to when they have to climb 60 to 100 meters up the wind turbine using the ladder. To insure that such lifts are safely and regularly maintained, certain safety mechanisms and testing methods are mandated by state and federal worker safety laws and standards. One such testing method is required for use with work cages and is referred to in the relevant art as the conventional “drop” test.
The drop test that is currently used with wind tower work cages is a time-consuming and arduous process which requires that weights be physically carried up ladders and hoisted into lifts that are situated above a landing or platform. Depending on the tower design, some platforms start at 10 meters up into the tower. Also, the weights that are to be placed are required to be provided at 125 percent of the maximum weight capacity of the work cage, or about 300 kilograms. The work cage is then raised approximately 1 meter from a landing and then dropped. Prior to this type of testing, the centrifugal brake must be removed from the motor/gearbox, which is also time-consuming. During the testing, maximum speed and drop distance is recorded. Following the testing, the centrifugal brake must be placed back into the motor/gearbox and the weights physically removed from the cage and then from the tower.
In the experience of these inventors, there is a need for an improved drop test method and apparatus which would eliminate the need to physically hoist, place and then remove test weights from the tower. It has been found that movement of 300 kilograms of “dead” weight within the turbine is unsafe. Further, all towers require that the weights be carried up steps and some towers require that weights be carried up 10 meter ladders. The weights create both pinch and strain risks and injuries have resulted from the movement of such weights. It is also expensive to transport such weights. In some instances, multiple vehicles are required to transport the weights, particularly where the towers are located in rural areas. Road conditions can result in delays in testing and the weights are also expensive to ship. Lastly, the movement of such weights increases inspection time. There is also a need to provide such an improved drop test where the time that would normally be required to perform the complete test is substantially reduced.